Automatic telephone-exchange system.



B. G. DUNHAM.

AUTOMATIC TELEPHONE EXCH'A NG E SYSTEM.

APPLICATION FILED, OCT. 5.1904.

Patented June 4, 19181.

mewm

5 SHEETS-SHEET l.

Ell THEE.

M23155 IE], E ljunham All B. G. DUNHAM.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION HLED 0CT.5| 1904.

m A M MW 0 mm Fl F1 Fl n n n n A m1 N ha M 3m w 3M @mm, m y G. B L w@ w fi Q l w w 2 u 5. L j

B. G. DUN HAM.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED OCT. 5.1904.

Patentvd Juno 4, 1918.

5 SHEETS-SHEET 3 m M 7 R w .0 7. .1 m mL a m u W D L Q B B. e DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

Patented Juno 4, 1918 4 0 9 i c 0 D E L H N 0 H A C H P P A 5 SHEETS-SHEET 4.

A Q (m 1 lilifi'llHh- BELDunham. G

' l V] I! N55555:

B. G. DUNHAM.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED OCT. 5. 1904.

1 268 921 0 Patented June 4, 1918.

5 SHEETS-SHEET 5.

G5 fim. ATTORNEY.

BERT G. DUNHAM, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

WESTERN ELECTRIC COMPANY, INCORP ORATED, A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented June c.1918.

Application filed October 5, 1904. Serial No. 227,286.

phone-Exchange Systems, of which the following is a specification.

My invention relates to automatic telephone exchange systems; that is, those systems wherein the connection between any two lines is'made by automatic switches at the central oilices, these switches being directed in their action by mechanism at the subscribers station under the control of the subscriber who desires to make a call.

In systems of the kind installed at the time of my invention, all the vertical and rotary relays of all the switches, are included in series in their respective line wires; and as a result, the talking circuit contained these relays in series. In a system adapted to serve all numbers under ten thousand, there would be two magnets included in series in the line at the first selector, two the second selector, two at the connector, and two in the first selector switch of the line being called, thus making eight electromagnets in series in each talking circuit between two subscribers. The'including of these magnets in series in the talking circuit was disadvantageous because of the fact that such magnets contained a certain amount of impedance, which in itself was deleterious to the talking eiiiciency. In order that this impedance might be as small as possible, it has been found necessary to wind the coils of these magnets with as few turns as is consistent with the mechanical duties they are to perform, and also to lace over the core of each magnet a copper s ield to further reduce the impedance of the magnets. As a result of their having a comparatively small number of turns, and the current available being limited by the resistance of the line wire, it followed that in many cases the magnets were not able to exercise a suilicient pull to accomplish their desired functions when energized over some of thelonger lines. The presence of the copper shield over the cores also tendedto make the-magnets slower in thelr action, and therefore they did not always respond to the rapidly recurring impulses sent over the line by the subscriber. It is the doing away with all series magnets in the talking circuit that is the object of my invention, and in accomplishing this I not only secure a more perfect talking circuit, but obtain a much more positive action of the relays, in response to much more rapidly recurring impulses than was before available. Furthermore the system is cheaper in that fewer relays and less complication of parts are required, and there is also less liability to cross talk between adjacent circuits than in the prior systems.

My invention is illustratedin the accom pa'nying sheets of drawings, which form a portion of this application, and in which- Figure 1 is a simplified circuit drawing showing the arrangement of relays involved in my present invention.

Fig. 2 shows the circuits at the subscribers station adaptable for use with my invention.

Fig. 3 is a diagrammatic re resentation of the features of the side-switch employed. Fig. 4 shows the circuits of a calling subscribers selector switch;

Fig. 5, the circuits of a second selector switch;

' Fig. 6, those of a connector switch, and

Fig. 7, the circuits of a first selector switch of a line that is being called.

Like characters refer to like parts throughout the several views.

In Fig. 1, is shown in simplified form the talking circuit of my im'proved system. From this it will be seen that the vertical and rotary relays of each' switch involved in the connection, are bridged across the circuit instead of connected in series therewith as in the prior art, and that from a point between the vertical and rotary relays in each switch there is a connection to the ungrounded pole of the battery, B. Two condensers, K K, are inserted 1n the respective lines of the talking circuit at the connector switch, the purpose of which will be pointed out later 0 An understanding of the circuits of the subscribers station may be had by reference to Fig. 2. The talking apparatus, consisting of a receiver, transmitter and induction'coil, may be connected between the vertical and rotary limbs of the line, V and B, respectively, by the action of the hook switch, 3, in a manner well understood. nder normal conditions, that is, when the ground connections at the subscribers station are primarily controlled at the pair of contacts, ,7, these contacts belng. held open as long as the receiver is on 1ts' hook, and

after the receiver. has been removed, until the impulse transmitting device has been put into operation.

The impulse transmitting device acts by causing the springs, 8, or 9, to engage the ground spring, 10, according to whether 1mpulses are to be sent over the vertical or rotary sides of the 'line. That is, if six impulses are to be transmitted, the spring, 8, will be pressed against the spring, 10, six times, thus allowing that many impulses to flow from the central oflice over the vertical side of the line to ground. It is obvious from the presence of the spring, 4 that no such impulse 'cantake place unless the receiver has been removed from its hook, and the impulse transmitter operated, for only under these conditions can the contact between springs, 7 be closed. In a similar manner an impulse over the rotaryside of the line may be secured by pressm the spring 9, against the spring, 10. It s iould be remembered that all selecting is done over the vertical side of the line b sending a series of impulses correspon ing to the digits belongingto the number of the subscriber wanted. Each series of impulses over the vertical side of the line caused by the movements of the spring, 8, is followed by a single impulse over the rotary side of the line caused by the movement of the spring, 9.

When the hook, 3, is depressed at the close of the conversation, its arm, 11, serves to press the springs, 12, 13 and 14, momentarily into engagement with each other before springs 7 are separated, thereby grounding both the vertical and rotary sides of the line through the springs, 14,

and the contact, 7. The mechanical arrangement of parts is such that the springs, 12, 13 and 14, are not brought into engagement with each other as the hook rises, or while it is either depressed or elevated. When the receiver hook is raised, it also serves to complete the transmitter circuit (by means of 1 contacts operated as indi-' cated) through the local battery used to supply talking current to the transmitter.

15 is the spring actuated by the ringing button, this spring normally .bearing against spring, 16, and serving to hold closed the talking circuit. When, however,

the ringing button is depressed, the spring, 15, engages spring, 17, thereby grounding the vertical side of the line for the operation of the ringing relay in the connector switch.

Referring now to Fig.4, the limbs, V and R, extending from the subscribers station shown in Fig. 2, may be seen entering the left of Fig. 4, where they are similarly lettered. B is a source of direct current, preferably a storage battery of about 25 cells, and giving from 50 to 6.0 volts, according to its state of charge. One of the poles of this battery is grounded, and between its live pole and the vertical side of the line is connected the coil of the vertical relay, VR, this connection including the springs, 18, 19 and 20 of the bridge cutoff relay, CO, these springs being normally held together. Connected in a similar manner in respect to the live pole of the battery, B, and the rotary side of the line, is the rotary relay, RR. It will be seen from this that, except when the bridged cut-ofl' relay, ()0, is energized, a path for current is afforded from the live pole of the battery, through the vertical and rotary sides of the line respectively, and therefore, when either the vertical or rotary side of the line is grounded at the subscribers station, a

path will be afforded through the corresponding relay of the first selector, thereby bringin about its energization.

The first series of vertical impulses sent by the subscriber is, as before stated, over the vertical side of the line, and the vertical relay, VB, is therefore caused to attract and release its armature in'accordance with these impulses. This causes corresponding periods of contact between the ground spring, 21, and spring, 22, which causes a flow of current through a circuit including the battery and the vertical magnet, VM, which maybe traced as follows: from the live side of the battery, through the coil of the vertical magnet, VM, to the point, 26", switch lever, 25, contact springs, 29 and 30 of the private magnet, PM, and through the springs, 22 and 21, to ground. Each impulse of current over this circuit causes the vertical magnet to lift the shaft one step.

The local circuit .just traced included the switch arm, 25, and its contacts 26. This arm forms a part of what is called a side switch, this consisting, in a first selector, of five arms, all coupled together, each arm being adapted to move over three contacts. For the sake of clearness in the diagrammatic illustration, these .-..ve arms are shown separated from each other, and are designated 25, 25", 25, 25, and 25*. The contacts which these arms engage are designated by the numerals, 26, 27 and 28, each with the letter corresponding to .its switch arm affixed thereto. This side switch performs important functions on all of the switches, and its action with respect to the first se-v lector switch will now be described.

The switch arms, 25, 25 etc., are subject to the tension of a spring which tends to move them from their normal contacts, 26, 26*, etc., toward the contacts, 28, 28*, etc. They are normally prevented from making this movement, however, and are held in their normal position by means of an escapement operated by the armature of the private magnet, PM; this relation being such that, when the private magnet is operated once, and released, the switch arms of the side switch will move one point; that is, the arm, 25*, will move from the contact, 26 to the contact, 27 all of the other arms making corresponding movement. A second attraction. and release of the private magnet armature will allow the spring to move the side switch levers from contact points, 27, to points, 28. The side switch arms will be finally restored to their normal position, which is that shown in Fig. 4, when the disconnect or release magnet, DM, is operated; and after being moved to this normal position, they will be retained there by the escapement of the private magnet, as before stated. I

Fig. 3 illustrates diagrammatically the mechanical features of a side-switch adapted to carry out the operations attributed to it. In this figure the same reference characters are used, where possible, as those used in the other figures. No attempt is made, in this figure, however, to-illustrate associated parts which are not directly concerned in the operation of the side-switch. Thus, for example, the private magnet, PM, is shown Without the contacts 29, 30 and 98 which, in fact, are associated with his magnet as shown, for example, in Fig. 4- The rotatably mounted shaft, 201, carries the sideswitch levers 25*, 25 etc., only two of which are shown, however. The associated contacts are shown at 26*, 27 28, and at 26 27 and 28 The arm, or lever, 202,having a triangular cross-section is rigidly mounted upon the shaft, 201. The private magnet, PM, is provided with an armature, 203, pivoted' at 204 and having an arm 205, extending toward the lever, 202. A spring, 211, cooperating with a sprlng arm, 212, tends to cause a rotation of the side-switch shaft and its switch arms in the direction of the arrow, 213. Thus upon the energization of the private magnet, PM, the arm, 205, is depressed and this causes the tooth, 206, on the escapement arm to strike the top of the tooth, 210, on the spring member, 208, this member because of its springy characteristics being held by its engagement with lever 202 and not, therefore, being affected by the movement of the armature 203.

22 1 tit.

When the arm 205 is depressed to cause the tooth 206 thereon to strike the top of the tooth 210 on the spring member 208, the spring member is thus effectively forced out of engagement with the escapement arm, 202. The face of the tooth, 206, is only slightly to the left of the face of the tooth, 210, so that the substitution of the tooth, 206,

'to retain the escapement arm, 202,:in its position in place of the tooth, 210, does not permit any material rotation of the sideswitch shaft due to the tension of the spring, 211. When, however, the deenergization of the private magnet, PM, permits retraction of the armature, 203, due to the influence of the spring, all, the face of the tooth, 210, will not engage the front surface of the escapement arm, 202, and this arm and shaft will be permitted to turn to the left under the influence of the spring, 211, until it strikes the face of the tooth, 209. So, also,

a subsequent energization of the private magnet, PM, will first cause the tooth, 207, to be substituted for the tooth, 209, to retain the side-switch shaft in its position, and then upon the deenergization of the private magnet the side-switch shaft will be caused to move a step farther in advance. The wire, 215, which is connected with the arm, 212, passes through a hole in the rigidly supported guide, 216, and is provided with an ad ustable stop, 217, by means of which the forward rotation of the side-switch shaft is limited.

The restoration of the side switches and the shaft upon which they are mounted to their normal position is brought about by the energization and subsequent deenergizzu tion of the disconnect-magnet, DM. In ad dition to the mechanism associated with this magnet for causing restoration of the shaft,

31, to its normal position, the armature, 218, of the magnet, DM, is provided with a catch, 219. The armature is pivoted at 220 and returned to its normal position by a eomparativelv stiff spring, 221. The wire, 215, which is quite springy, is provided at its end with a very thin, flexible plate, 222, this plate having a suitable opening at The vertical magnet, VM, is equipped with an armatlll'c,'22l:, pivoted at 225, and provided at its extremity with a catch, 226. The energization of this magnet, VM, raises the armature, 22-1, and by means of the catch, 226, it raises also the plate, 222 disengaging it from the restraining influence of the catch, 219, and makzug the rotation of the sideswitch shaft, 201, subject only to the operation of the escapement associated with the rivate magnet, PM.

The restoration of the selector mechanism upon the energization and dcenergization of the disconnect-magnet, DM, restores the plate, 222, to the position shown in Fig. 3. When next this particular mechanism is 130 'tivel y.

called into service the first ener ization of vertical magnet, VM, immediateTy releases the plate, 222, from the catch, 219, and puts the side-switch under the control of the escapement associated with the private magnet, PM.

The first set of impulses sent over the vertical line, caused, as has been shown, the stepping up of the shaft, the number of steps corresponding to. the number of the first digit in the line designation of the called subscriber. The shaft of the first selector is shown in Fig. 4, at 31, it carrying three winers, 32, 33 and 34. NVipers 32 and 33, are adapted to engage pairs of stationary contacts, such as 37. and 38. But one pair of contacts is shown as being terminals, in this particular first selector, for the two limbs, 35 and 36 of the trunk line, extending to the second selectors, these limbs being also connected to other pairs of contacts, 37", 38", 37, 38, etc, on other first selector switches.

The wiper, 34, carried by the shaft, 31, may engage successively contacts of which 39, is one, these contacts being multipled to corresponding contacts on other first selector switches, such contacts being shown as 39, 39, 39, etc. These contacts are termed private contacts for reasons that will be pointed out later, and there are as many of them in each selector as there are pairs of trunk contacts. They have no trunk connections, and each contact is engaged by the wiper, 34, at the same time that the contacts, 37 and 38 are engaged by their wipers, 32 and 33.

Immediately after the cessation of the first series of impulses over the vertical line, a single impulse is sent by the subscribers transmitting mechanism over the rotary line, this causing the rotary relay, RR, to give its armature one impulse, the circuit over which current fiowsto cause this action being traced from the live side of the battery, through springs, 18 and 19 of the bridge cut-off relay, CO, coil of the rotary relay, RR, to the rotary side of the line and the ground at the subscribers station. The eneroization of the rotary relay, RR, causes the spring, 40, to engage the spring, 21, thus closing a circuit through the private magnet, PM, traced from the live side of the batterv, through this magnet, springs, 40 and 21, to ground. The operation and immediate release of the private magnet thus brought about, serves no other purpose than to release the side switch one step. The side switch levers, 25, 25*, 25, 25, and 25*, therefore move into engagement with contact points, 27, 27, 27, 27 and 27, respec- The moving of the side switch into this position, brings about three results: first, to close a circuit through the rotary magnet, which may be traced from the live side of the-battery through the coils of the rotary magnet, RM, the side switch arm, 25, thence through the contact point, 27 of the side switch, to the interrupter, 41, and thence to ground. Current flowing through this path is interrupted repeatedly by the interrupter, .41, which is driven by any convenient source of power; and in this way a rapid succession of impulses is given to the shaft, 31-, so that the wiper contacts engage in rapid succession the bank contacts in the row opposite which they have been brought by the vertical magnet. This rotary motion on the part of the shaft will stopas soon as the wipers engage the contact of an idle trunk line in a manner that will be pointed out presently.

The second result of the moving of the I side switch to its middleor second position is to disconnect thetwo line conductors, V and R, from their branches to bank contacts of connector switches; in this position of" the side switch, the line conductors are open at the levers, 25 and 25.

The third result brought about by the moving of the side switch into this second position, is the connection of the private wiper, 34, to the live side of the battery throu h the switch arm, 25 contact, 27, an

coil oi the private magnet, As soon as any trunk line becomes busy by virtue of being connected with at any first selector switch, all of its private contacts, such as 39, 39", 39, and 39, are connected to. ground. This is true because a first selector switch that has completed its connection with a trunk line, holds its side switch on the third set of contact points; that is, the side switch lever, 25, of such a first selector will be upon contact, 28, and therefore all of the private bank contacts of a busy trunk line are grounded in this manner.

Coming back now to the rotary movement of the shaft, 31, under impulse of the rotary magnet, RM, it will be seen that, while the private wiper, 34, is moving over the rivate bank contacts of busy trunk lines, t e private magnet will be receiving current over a circuit which may be traced from the live side of the battery, through the coil of the private magnet, contact, 27, switch lever 25, to wiper 34, and thence to ground through the private bank contacts, such as 39, corresponding to busy trunk lines, and to ground by means of the. wiper, 34, the switch arm, 25, and contact, 28, of the first selector switch that is at that time connected withthe trunk line. As soon as the "wiper, 34, of the first selector that is rotating in search of an idle trunk line, finds a contact such as 39, corresponding to an idle trunk line, no ground willbe present on such contact, and as a result the circuit through the private magnet will be broken, and it will allow its armature to fall back. This is all that is needed to allow the side switchto move to the third position, so that the contact levers, 25, 25",-25, 25 and 25, will engage the corresponding contact points, 28 28", 28, 28, and 28. Thevertical and rotary sides of the line are now, as clearly shown in Fig. 4, continued through the side switch levers, 25 and 25, to the wires leading to the wipers, 32 and 33, and should now engage a'pair of contacts-such as 37 and 38 of some trunk that until now was not busy. Meanwhile the wiper, 34, has eng'aged the private contact such as 39, and this, together with all of the other private contacts belonging to that trunk line on the first selector switches, is grounded through the side switch lever, 25, and its third contact, 28, thus holding this trunk line busy to all subsequently operated first selectors which try to obtain a-connection with it.

I have now traced the action of the first selector in making a connection between a. calling subscribers line and the two sides, 35 and 36, of a trunk line, leading to a second selector. This trunk line may be seen entering the second selector at the lefthand side of Fig. 5, and a study of the circuits will show that the vertical and rotary relays VR" and RR, of the second selector now occupy the same relation with'respect to the battery, and the two sides, V and R, of the line respectively, as do the vertical and rotary relays of the first selector. The second set of impulses over the vertical side of the line sent by the subscriber in operating his transmitting device, will cause the operation of the vertical relay, VR', stepping up the shaft, 42, of the second selector by virtue of its causing impulses to be sent through the vertical magnet, VM, over a path traced from the live side of the battery, through the coil of the vertical magnet, VM, contact 46*, and arm 45*, of the side switch, contacts,- 49 and 50, of the private magnet, PM, contacts, 51 and 52, of the vertical relay, VR', to ground. The immediately succeeding impulse over the rotary side of the line causes a single attraction and release of the armature of the rotary relay, RR, which causes a flow of current through the private magnet, PM, over a circuit traced from the livejside of the battery, through this magnet to the contact, 53, and thence to ground through contact, 52. This single cycle of the private magnet releases the side switch, which moves to its second point, and this, as before, connects the rotary magnet, RM in a local circuit including the battery, B, and the interrupter, 41, thus stepping the shaft, 42, around until the pri-' vate wlper, 54, engages a private bank contact, such as 55*, that is not grounded. As long as the private wiper, 54, enga es a private bank contact that is grounde by virtue of the trunk line to which it belongs becurrent will flow/from the battery,

net and stopping the rotation of the shaft.

At'the same time ground will be put on all .of the private contacts of this trunk line,

through the side switch arm, 45, and its contact, 48"; the two trunk lines, 35 and 36,

- formingna continuation of the calling sub scribers line, will also be continued through the contacts, 48 and 48 to the wipers, 56 and 57 respectively, and thence through bank contacts, 58 and 59 of the trunk line selected to the twosides, 60 and. 61 respectively, of the trunk lines leading to the group having connectors serving the group of 100 lines in which the line of the called subscriber belongs.

The two limbs, 60 and 61, of the trunlt line between the second selectors and the connector chosen, may be seen entering this connector at the left hand of Fig. 6. This places the vertical and rotary relays, VR and BB of the connector in exactly the same relation with respect to the limbs, V and R, of the line, and the battery, B, as existed with respect to the vertical and rotary relays of the first and second selectors. The vertical and rotary relays of the connector are therefor subject to impulses caused by the manipulation of the switch at the subscribers station in exactly the same manner as are the corresponding relays of the first and second selectors. The third series ofv impulses passing over the vertical side of the line, and its continuation of limbs, 35 and 60 of the trunk, causes the vertical relay, VH of the connector to close its contact spring, 62, against the spring, 63, and thereby operate the vertical magnet, VM over a circuit traced from the live side of the battery, B, through the coil of this magnet, to the contact and lever, 66 and of the side switch, to the springs, 69 and 70, of the private magnet, PM, springs, 62and 63, of the vertical relay, to ground. The immediately succeeding impulse on the rotary side of the line now formed by the line, R, with its extensions,

.36 and 61, causes a single attraction of the causes the operation of the private magnet, I

PM over a circuit traced from the live side of the battery, through the coil of this magnet, sprlng, 71, of the rotary relay, to spring,

the vertical magnet. The closure of contact points, 62 and 63, of the vertical relay will, under this condition, cause current to flow. from the live side of the battery, B, through the rotary. magnet, RM contact, 67 of the side switch, lever 65 of the side switch, contacts, 69 and 70 of the private magnet and contacts, 62 and 63, of the vertical relay to ground. As a result, therefore, the shaft of the connector will be rotated in response to the'fourth series of impulses sent by the subscriber as many steps as there are impulses in this series. The impulse over the rotary side of the line which immediately succeeds 'thelast of the series of impulsesover the vertical sideof the line causes the rotary relay, Rld to close 1ts contacts once.

The closure of the contact, 71, against the.

contact, 63, completes the circuit containing the private magnet which is again operate and causes the side switch to move toits third position. The moving of the side switch into the third position extends the vertical and rotary lines, and 61, containing serially the condensers, K and K, respectively, to the wipers, 72 and 73, this connection being brought about through the side switch levers, 65 and 65, and the corresponding contacts, 68 and 68. As the wipers, 72' and 73, in response to the last series of impulses sent over the vertical'side of the line, are brought into engagement withthe contacts 7 5- and 7 6, respectively, of the subscriber s line that was called, it follows that the circuit from the calling subscribers line to the called subscribers line is now complete, and a study of the cirvcuits will reveal the condition shown in Fig. 1.

The line circuit is then continued from the wiper contacts, 72 and 73, through the connector contacts, 75 and 7 6' and by means of wires, 94 and 95, to the first-selector of the line called. The circuits showing the connection of these wires, 94: and 95, through the first selector to the vertical and rotary sides, V and R, of the line called for, are shown in Fig. 7 where the wires, 94. and 95, may be seen entering at the left, and the line wires, V and R, of the subscriber called, extending at the right. Triasmuch as the first selector of the line called for 15 at normal, the side switch of that selector is at its normal point, and connecmeager tion of the wires, 94 and 95, to the respective wires, R and V, of the called subscriber is therefore through the side switch lever, 25, and its contact, 26, in the case of the rotary side of the line, and through the lever, 25, in the case of the vertical side of the line.

It is in the case of the first selector of the line called for that the bridge cut-ofi' relay, CO, to which no use has yet been assigned, comes into play. When a line is called, and is connected to by a connector, a circuit is established through the bridge 'cut-ofi' relay of the first selector of that line, which causes the energization of that relay. This circuit may be traced in Fig. as follows from thelive side of the battery, "through the bridge cut-0H relay, CO, conta'ct,,26,' and lever, 25, of the side switch, thence by the wire, 96, to the private bank contacts, 84 and 84 of theconnector switch which is connected with the line. This connector switch has its side switch at that time in the third position, and therefore this circuit may be traced through the wiper, 85, of the connector switch, (seeFig. 6), lever, 65 contact 68, of the side switch of that connector to ground. This operates the brid e cut-ofl' relay, and causes a separation o the contacts, 18, 19 and 20, thus cutting ed the vertical androtary relays from the battery, and from connection with each other, and reducing the number of bridges across the line by one.

At the righthand side of Fig. 6, are shownthe rnultiple contacts for both line and private banks of the connector, and at the leftlfand side of Fig. 7, is shown the way in which these connector contacts for any line are connected with the first selector of that line. This connection is also indicated in Flg. 4:, the connector contacts, both line and private, being shown in the lower lefthand corner of this figure.

It now only remains to call the subscriber desired, and this is accomplished by the subscriber pressing the ringing button shown in Fig. 2, which causes spring, 15, to engage sprin 17, thereby grounding the vertical side, of the line. Current 1s then caused to flow from the battery,B,through the vertical relay VH of the connector, over the wires, 60 and 35, to the vertical side, V, of

the line, and thence to ground through contact springs, 15 and 17. The operation or the vertical relay causes a circuit to be closed does an ordinary ringing key, in a manually operated exchange. The circuit of the line is cut off by the breaking of contact between springs, 77, and. 78, and also 79 and 80, and establishes circuit between the called line and the generator, 81, by causing the springs, 78 and 80, to make contact with the springs, 82 and 83, respectively. Calling current is thus sent to the' line of the subscriber called, and his bell, bridged across the circuit of the line, is rung in the usual manner.

If another subscriber desires to make connection withhthismsame subscriber that has just been called, the connector switch employed by him in completing the final link toward connecting with this line will, when it attempts to stop on some of the-connector bank contacts, such as 75 and 76", or 75 and 7 6, be met with the condi tion that the corresponding private contact, 84' or 84, is grounded through the private wiper, 85, side switch lever,-65 and side switch contact, 68. Such a connector switch attempting to stop upon the connector colitacts of a line that is held busy at another connector, would at once be released for the following reason: The connector switch attempting to make this connection will have its side switch on the second position; and therefore its private wiper, 85, will'be connected through the side switch lever, 65, and contact, 67 to the spring, 87, of the rotary relay, RR When, therefore, the final rotary impulse goes over the wire, 61, the rotary relay is operated once, and this operates the release'or disconnect magnet, DB

by closing together the contacts, 86 and 87,

this circuit being traced from the live side of the battery, through the disconnect relay, DR and tl1e,.contacts, 87 and 86, contact, 67, and lever, to the private wiper, 85, which rests at that time upon a grounded privatecontact, 84* or 84 As a result the disconnect magnet, DB is operated and the connector falls back to its normal position. This meansthat the shaft, 7 4;, of the connector of a party who thus fails to secure the line because it is already connected to b another connector, occupies its normal position. The subscriber who makes the call does not know yet that he has not received the de sired connection, and he presses his ringing button. This grounds the vertical side of his line and operates the vertical relay, VR which in turn operates the vertical magnet, VM to raise the connector shaft one step, or as many steps as the number of times he presses his ringin key. The connector shaft is .itheref0re off normal, and this means that the spring, 88, makes contact with thespring, 89. These. two springs are always held out of engagement witli each other, while the shaft is in its normal position, but are brought together as soon as the shaft is raised one step. The closure of the contacts, 88 and 89, of the connector. throws a tone, or busy. upon the line, this being produced in the following manner: The numeral, 90, refers to a constantly revolving contact wheel, against which two brushes rest, this contact wheel being bridged by a condenser, 91, having an approximate capacity of 4 microfarads. B is an auxiliary or test battery of low voltage, from L} to 3 volts, the circuit of which is interrupted by the alternate segments and insulation blocks of the contact wheel, 90. A lamp resistance, 92, is placed in circuit with the contact wheel, and battery, B, to reduce the flow of current to proper degree. When, therefore, a subscriber attempting to make a connection, as has been described, andfailing to do so, because the line called for is already connected with, the closure between springs, 88 and 89, throws interrupted current from the battery, B, across the line, this being traced from one pole of the battery, B, to the main battery lead, extending to the rotary relay,

RR over the coil of this relay to the wire,

61, thence to the wire, 86, and limb, R, of the line, through the telephone of the waiting subscriber, back by the limb, V, of the line wire, 35, wire, 60, condenser, K, through the contacts, 77 and 78 of the ringing key, to the switch arm, 65, and contact, .66 of the side switch, by wire, 93, tothe springs,

89 and 88, to lamp, 92, thence through the contact wheel, back to the other pole of the battery, B. Several shunts exist through the various relays bridged across the line at the central oflice, which serve to some extent to cut dc/wn the loudness of the tone that is produced, but a sufficient tone is heard by the subscriber to notify him that the line is busy.

It now remains to show how the line is released at the end of the conversation. The release is accomplished by the act of the subscriber who made the call, hanging up his telephone. This momentarily grounds both sides of the line by causing the springs, 12, 13 and 14, Fig. 2, to engage each other; current then flows from the battery, B, through the vertical and rotary relays of each switch, used in building up the connection, to the vertical and rotary sides of the line respectively and then back to battery through ground. Both the vertical and rotary rclays of each switch are therefore operated simultaneously, and the clearing out is accomplished in practically the same manner in all of the switches, and will, therefore, be described with respect to the first selector only.

Referring to Fig. 4, the operation of the rotary relay, RR, will close together the springs, 21 and 40, and thus complete a circuit through the private magnet. The private magnet when operated will cause the spring, 30, to engage the spring, 98, which the holding pawls 'from both the vertical and rotary ratchets on the shaft, which therefore returns to its normal position by the actions of its spring and gravity.

Both the first and second selectors have pairs of contacts, 99 and 100 respectively, which are held apart as long as the shaft of the corresponding selector is in its normal position, but are closed together as soon as the shaftis raised one step from its normal position. These pairs of spring contacts are known as 0E normal switches, and serve to complete the circuit through lamps, 101" and 102*, which lamps may be common to a group of selector switches, and which when lighted serve to show merely that some selector inthat group is f oil normal.

The relay, 101, in Fig. 6, enables a subscriber who has been called to disconnect from his line that of the callin subscriber, and this disconnection is eflecte at the connector switch which established the previous connection. To secure such a release the called subscriber hangs up his receiver, an in. so doing, momentaril actuates spring 12 to cause said spring an the springs 13- and 14 to connect together, thereby grounding both sides of the line. This will actuate both relays 101 and 102, thus ounding springs 104 and 105. This grounding of the spring, 105, will immediately actuate the disconnect relay, DR, withdrawing the pawls of the connector switch, and allowing its shaft to return to normal position.

The relay, 102, serves another oflice than the described one of assisting to disconnect the connector switch, and it'is that of enablin a subscriber who has been called for a tol? line connection, to transmit signals to the toll switchboard. The convenient method for handling this toll service is to provide the toll operators with lines to the automatic mechanism, quite as if they were subscribers lines, and to. provide the toll operators further with mechanism by which signal impulses may be sent over the trunk lines. The subscriber having been called for the purpose of a toll line conversation, he may desire to recall the toll operator, and must signal for disconnection when the conversation is completed. He does this b pressing his ringing button, which wi nacaaar ground the conductor, 95, of his line, and under the existing conditions, the contact wiper, 73, the point, 68, thelever, the spring, 80, and contact, 79, and finally the terminal of the relay, 102; as the other terminal of this relay is connected to the live side of the battery, the relay will operate;' contact between the springs, 103 and 104, will then establish a ground connection through the resistance, 105, conveniently about 500 ohms, and thence to the line conductor, 61. The springs 103 and 104 may control a circuit including a signal at the toll board which will actuate whenever relay 102 is energized' It will be seen from a consideration of the foregoing description, and the illustrations to which it refers, thateach of the line relays, such as VB and RR, VR' and RR, etc., are means at the central ofiice by which the subscriber controls the operation of the various selectors and connectors. The mag nets of these controlling relays may, therefore, be termed controlling magnets, and it will be seen that in all cases they are bridged across the circuit of the subscribers line, or

of the trunk line to which the corresponding selecting switch belongs. This is not only true in the case of the line or trunkcircuits when separately considered,but in the case of all built-up connections formedby attaching any trunk to any line, or any line to an trunk, as in such built-up circuits the air of controlling magnets used in bringmg about the connection remains bridged across the combined circuit of the line and d trunk.

The controlling magnets of each selecting switch that is employed actively in building up a circuit between any two lines, or between any l ine and any trunk, whether these selecting switch'es be selectors or connectors, are left bridged across the talking circuit so formed, and thus afiord a means for restoring all of the switches to their normal positions at the close of the conversation, by the simultaneous operation of all of the controlling magnets actively employed lin building up the connection.

It will also be seen that the side switch, according to the position it is in, serves to vary the functions of the controlling magnets of each selector. For instance, in the case' of the first selector, when the side switch is in its first position, the vertical relay directly controls the circuit of the ver tical magnet. When the side switch is in its second orthird positions, the vertical relay has'no control over the vertical magnet.

It is evident that the wiper contacts carried on the shaft of each selector or connector, may be referred to as selecting contacts, since they are the contacts actively employed to pick out any of the bank contacts within their reach. Similarly, the various bank current, substantiallyas described.

line extending substation, se e 1 station for extending the circuit of said line "through the central oflice, a sourcq of current .scribers line, a

contacts 'within the range of any pair of selecting contacts or wipers, may be referred may be made in these respects without departing from the spirit of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is: -1. In a. telephone system, a metalllc clrcuit from a central station to a cting switches at the central a the central station, controlling magnets for each selecting switch contained in bridge paths across said metallic circuit when said line is extended through the central oflice, a

third conductor, and meansat the substation for energizing said controlllng magnets over a limb of thesaid metallic circult and said third conductor, substantially as described.

2. In a telephone system, a metallic circhit line extending from a central station to a substation, a plurality of selecting switches at the central station having series contacts for extending the circuit of said line, a sourceof current at the central station, a plurality of controlling magnets, one Er each'of said selecting switches, connected i parallel between one limb of said metallic p ircuit and a terminal of said source of cur- ,ent when said switches are connected in series, another controlling magnet for each ofis'aid selecting switches connected-between theRothcr limb of the line and the same ter-' minal of said source of current when said switches are connected in series, and a return path for the other terminal of saidsource, of

3. In an automatic telephone system, a metallic circuit subscribers line, a selecting switch in which said line terminates, a met'allic circuit trunk line which said selecting switch is adapted to, connect to said sub- .for said switch ridged across the limbs or the talking circuit formed by said subscrib-- ers line and the connected trunk line, a source of current adapted to supply current to the limbs of said subscribers line through thecoils of said magnets, and means at the substation for controlling the circuit through said magnets for causing the operatlon of said switch, substantially as described;

4. In a telephone system, a central station, two substations, selecting switches in sald central station, a metallic talking circuit joining said substations through said centralsaid central station,

air of controlling magnets.

' substation,

station, a source of current, magnets controlling said selecting switches and connected in bridge across said metallic circuit,means at one of said substations adapted to effect the ener ization of said magnets by said source 0% current, and two condensers in one serially connected in each of the conductors of said metallic circuit, substantially as described.

5. In a tele hone system,

a pair of metal- 110 clrcult su scribers lines leading to a central oflice, selecting switches at said central ofiice, trunk lines controlled by said selecting switches for connecting said pair of lines together, a pair of controlling magnets at each of said selecting switches simultaneously bridged'across the talking circuit between said two stations, a source of current adapted to supply current to the limbs of said line through said magnets, and means at one of the'subscribers stations for 010s ing the circuit through said magnets for the described.

6. In an automatic telephone system, a metallic circuit line, a third conductor, a first selector therefor, and a group of trunk lines to any one of which said first selector is adapted to connect said line, a pair of controlling magnets for said switch bridged across the talking circuit of said line as which said first selector is adapted to connect said line, a source of current, a magnet for said switchconnected between one'limb of said line as extended through one of said tru'nk lines and said source of current. an other magnet for said switch connected between the other limb of said line and said source of current, a third conductor, a substation for said line, and means at said substation for closing the circuit between either limb of the line' and said third conductor for causing the operation of said magnets to control said switch, substantially as described. A

8. In an automatic telephone system, a a metallic circuit line connecting said substationto a central oflice, a thi'id conductor, a selector and connectors at said central office, a plurality of groups of waiting contact points through any one of which said selector may extend said line to one operation of said switches, substantially as tit) of said connectors, a controlling magnet at said selector connected in a l)I'l( ge across the talking circuit of the line during conversation, a source of current connected between said magnet and said third conductor, means at the substation for connecting said limb with said third conductor to actuate said magnet to cause said selector to pick out one group from the plurality of groups.

9. In an automatic telephone system, a substation, a metallic circuit line connecting said substation to a central otlice, a third conductor, a selector and connectors at said central office, a group of waiting contact ooints through any one of which said selector may extend said line to one of said connectors, a controlling magnet at said selector connected in a bridge across the talking circuit of the line during conversation, a source of current connected between said magnet and said third conductor, means at the substation for connecting said limb with said third conductor to actuate said magnet to start said selector in its action of selecting one contact of said group of waiting contact points, substantially as described.

10. In an automatic telephone system, a substation, a metallic circuit line connecting said substation to a central oliice, a third conductor, a first selector at said central otl'ice, selecting contacts in said selector, a group of waiting contact points to any one of which said selecting contacts may extend said line, other groups of contact points to which the contact points of said first group are multipled, a controlling magnet for said selector connected in a bridge across the talking circuit of the line during conversation, a source of current connected between said magnet and said third conductor, means toactuate said magnet to start said selector, and means for continuing the movement of said selecting'contacts until anidle contact in said group is reached, substantially as described.

11. In an automatic telephone system, a substation, a metallic circuit line connecting said substation to a central ollicc, a third conductor, a selector for said line. other automatic switches at the central office, se-

lecting contacts in said selector, a plurality of,groups of waiting contact trunks connecting the same to other switches, to any one of which said selecting contacts may extend said line, a controlling magnet at said selector, connected in a bridge across the talking circuit of the line during conversation, and adapted when energized to cause said selecting contacts to select one of said groups of waiting contacts, a second controlling magnet connected in a bridge across the talking circuit of the line and adapted when energized to control the mechani'sm for causing said selecting contacts to 1,aca,a21

pick out an individual waiting contact in 'limbs of said line with said third conductor to cause the energization of said controlling magnets, substantially as described.

12. In an automatic telephone system, a substation, a metallic circuit line connecting said substation to,a central oilice, a third conductor, a selector for said line, other switches at the central oltice, selecting contacts for said selector, a plurality of groups of i'aiting contact trunks connecting the same to other switches, to any one of which said selector may extend said line, a controlling magnet at said selector connected in abridge across the talking circuit of the line during conversation, and adapted when energized to cause said selecting contacts to se lect one of said groups, a second controlling magnet connected in a bridge across the talking circuit of the line and adapted when energized to contfol mechanism for causing said selecting contacts to pick out an individual waiting contact in said selected group, a source of current connected between said magnets and said third conductor, and means atthe substation for connecting either limb of said metallic circuit line to the said third conductor to cause the actuation of said magnets, substantially as described.

13. In an automatic telephone system, a substation, a metallic circuit lineconnecting'said substation to a central office, a first selector at said central office, other switches at the central office, a plurality of'groups of waiting contact points, conductors extending to said other switches, to any one of which said selector may extend said line, a source of current at said central office, a controlling magnet for said selector connected between one limb of said line and one terminal of said source of current during conversation, a second electromagnet connect/ed between the other limb of said line and the same terminal of said source of current, a return path for said source'of current, and means atthe substation for connectingsaid first limb of said lineto said "return forenergizing said first magnet, to cause said se-. lector to pick out one group from said plurality of groups, and further means at the substation for connecting said other limb of said line to said return for energizing said other magnet to cause said second magnet to actuate said selector to pick out one waiting contact from said selected group, substantially as described.

14. In a telephone system, a metallic circuit line, a selector therefor, other switches, selecting contacts, and a plurality of groups of Waiting contacts adapted to be engaged tllh llltl .vidual contacts in said group,

thereby, trunks connecting said contacts to said other switches, a magnet adapted to move said selecting contacts opposite a particular group of waiting contacts, another magnet adapted to start said selecting contacts in their movement of selecting indisaid pair of magnets being connected ina bridge across the talking circuit of which "said line and said selected contacts form a part, a source of current between said magnets and a third conductor, and means for closing the circuit through said source of current and either of said magnets to cause the operation of said selector switch, substantially as described.

15, In a telephone system, the combination with a pair of subscribers stations, of a talking circuit extending in two conductors between said stations, a plurality jof automatic switches having contacts connected in series for completing the connection between said subscribers stations, and 'a' plu rality of electromagnets connected with said talking circuit at each of said switches, the coils of said magnets being out of the path of voice currents between subscribers stations, and mea-nsat one of'said stations for energizmg all of said magnets in parallel to I release said switches.

16. In an automatic telephone system, a substation, a metallic circuit line, and a selector therefor, selecting contacts for said selector, and a plurality of groups of waiting contacts adapted to beconnected by said so e cting contacts, a magnet for said selector line, and means for causing said switch to connect said selecting contacts to said line after the desired waiting contact has been selected, substantially as described. 7 p 17. In an automatic telephone system, a

metallic circuit, a source. of current, a relay adapted to be'bridged across the talking c-ircuit of said line and connected between one limb of said line and said source, a return conductor for said source of current, a

pair of selecting contacts, a plurality of groups of waiting contacts adapted to be engaged by said selecting'contacts, a magnet controlled by said relay adapted to move said selecting contacts in the selection of a group of waiting contacts, a switch .for breaking the circuit of said magnet, a sec ond relay connected between the other limb of said line and said source of current, and

' through said selector,

I a ameans controlled by said second relay for operating said switch to prevent the further control of said magnet by said first relay,

5 contacts for said switch, a group of waiting contacts adapted to be selected by said selecting contacts, a relay bridged across the talking circuit of said line, and a source of current for operating said relay, a magnet adapted to cause said selecting contacts to pick out individual waiting contacts in said group, a source of periodically recurring current, a switch for closing said periodically recurring current through said magnet, and means controlled by said relay for operating said switch, substantially as described.

19. In a telephone system, the combination with a pair of subscribers stations, of a talking circuit extending in two conductors between said stations, a plurality of automatic switches having contacts connected in series for completing the connection between said subscribers stations, a plurality of'pairs of electromagnets, one pair connected with said talking circult at each of said switches, the coils of said magnets being out of the path of voice currents between subscribers stations, and means for simultaneously'energizing all of said magnets over a telephone line to cause the release of all of said switches.

, 20. In atelephone system, two substations, a central station, selector switches, a connector switch, a. metallic talking circuit con- :necting said substations through said central station, magnets for controlling said selector and connector switches bridge-d across said talking circuit, a source of current at said central station adapted to supply ourrent through said magnets to the limbs of i said metallic talking circuit, a return path for said source of current, and means at one of the substations for causing current to flow through all of said magnets simultaneously to cause the-breaking up of said talking circuit and the returning of said selector switches'to their normal position, substantially as described. A

21. In an automatic telephone system, a metallic circuit line, a selector therefor, selecting contacts in said selector, a plurality of groups of waiting contacts with which said selecting contacts are adapted to en gage, a pair of controlling magnets bridged across the talking circuit of said line means for operating said controlling magnets to respectively move said selecting contacts to pick out a group of said waiting contacts, and there-. after to pick out 'a contact in sai selected group, and a side switch for varying the functions of said pair of magnets, substantially as described.

22. In an automatic telephone system, a metallic circuit line, a third conductor, a substation, a selecting switch for said line at a central oflice, selecting contacts in said selecting switch, a plurality of groups of waiting contacts with which said selecting contacts are adapted to engage, a pair of magnets bridged across the talking circuit of said line through said selecting switch, a source of current connected between said magnets and said third conductor, means at the substation for completing the circuit through one of the said magnets over one limb of said line and said third conductor to operate said magnet to cause said selecting contacts to pick out a group of said waiting contacts, means at the substation for closing the circuit of the other of said magnets over the other limb of said line and said third conductor to cause said selecting contacts to pick out certain ones of said selected group of waiting contacts, and a side switch for varying the functions of said magnets, substantially as described.

23. In an automatic telephone system, a group of metallic circuit lines centering in a central station, metallic circuit trunk lines adaptedto connect said lines for conversation, a selecting switch for each subscrihers lineand for each trunk line, controlling magnets for each selecting switch adapted to cause said switches to interconnect said lines in pairs through said trunks, said magnets being bridged across the talk ing circuit of the line and trunk to which the corresponding selecting switch belongs during conversation, substantially as described.

24. In an automatic telephone system, a groupof metallic circuit lines centering in a central station, metallic circuit trunk lines adapted to connect said lines for conversation, a selecting switch for each subscribers line and for each trunk line, controlling magnets for each selecting switch adapted to cause said switches to interconnect said lines in pairs through said trunks, said magnets being bridged across the talking circuit of the line or trunk to which the corresponding selecting switch belongs, means at the subscribers station for operating said bridged magnets separately to build up a connection between two lines, and simultaneously to destroy said connection, substantially as described.

25: In a telephone system, a telephone line and selecting switches, a second telephone line having waiting contacts, a trunk line for connecting said telephone lines; a connecting switch for said trunk line, relays in bridge across the talking circuit during talking for controllingeach selecting swltch,

a side-switch for each selecting switch, means on one of said telephone lines for causing the relays in bridge on said lineto pick out said trunk line, means on said telephone line for causing said side-switch to continue the circuit of said line to circuit of said selected trunk line, means at the associated subscribers station for causing said selecting switch of said trunk line to pick out, and connect with the waiting contacts of said subscribers line, substantially as described.

26. In a telephone exchange system, the combination with a metallic telephone line, of a plurality of switches connected together to extend the talking circuit of the line, and magnetic means at each switch connected in a bridge of the talking conductors and adapted to bring about the release of that particular switch, substantially as described.

27. In an automatic telephone system, a substation, a metallic circuit connecting said substation to a central office, a lurality of switches at the central office having contacts in said circuit, a controlling magnet at each switch connected during conversation in a bridge across the talking circuit of the line, a central source of current for supplying energy to said magnet, and means at the substation for completing the circuit of said source through said magnet, substantially as described.

28. In an automatic telephone system, the combination with a telephone line of selector and connector switches at the central ofiice adapted to be picked up in succession in establishing a talking circuit through the exchange, electromagnets in a bridge of the talking conductors during conversation at the selector switch for controlling the operation of said switch, and electromagnets in a bridge of the talking conductors during conversation at the connector switch for controlling the operation of said switch, a central source of current, and means at the substation for suitably closing the circuit of said source through said magnets to control the operation of said switches, substantially as described.

29, In an automatic telephone system, a

first selector, a second selector,:and a connector having series contacts for extending a telephone line within the central office, and an electromagnet in a bridge of the talking conductors at each of said switches during conversation, to.-co'ntr'ol said switches.

30. In a telephone system, a selector and a connector havmg series contacts to extend the talking circuit, and a switch controlling electromagnet at each of said switches, bridged between the limbs of the talking circuit during conversation. u

31. In a telephoneexchange system, a pluralityof automatic switches having series till contacts extending the I talking circuit through the central office, electromagnets for the control of said switches, one bridged between the limbs of the talking circuit at each switch during connection.

32. In an automatic telephone system, the combination with a telephone line of a first selector therefor, having control magnets connected in a bridge between the limbs of the telephone line during conversation when said line is a calling line, and a cut-otf relay adapted tov interrupt the circuit of said bridge when said line is called.

33. In a telephone system, a metallic cir cuit line extending from a central station to a substation, selecting switches at the central station for extending the circuit of said line, a source of current at the central station, controlling magnets for each selecting switch contained in a bridge path across said metallic circuit as' extended through said switches, a third conductor, means at the substation for energizing said controlling magnets over a limb of said metallic circuit and said third conductor, and release means for each switch operated by the simultaneous energization of both of its controlling magnets.

34. In a telephone system, a metallic talking circuit extending in two limbs from a central station to a substation, a plurality of selecting switches at the central station for extending the limbs of said talkin circuit, a source of current at the centra station, ,a controlling magnet for each of said selecting switches simultaneously connected between one limb of said talking circuit and a terminal of said source, another controlling magnet for each of said selecting switches connected between the other limb of said talking circuit and the same terminal of said source, and a return path for the other terminal of said source.

35. In an automatic telephone system, a metallic circuit subscribers line, a selecting switch in which said line terminates, a metallic circuit trunk linewhich said selecting switch is adapted to connect. to said subscribers line, a pair of controlling magnets adapted to be bridged across the limbs of the talking circuit formed by said subscribers line and the connected trunk line, a source of current adapted to supply current to the limbs of said subscribers line through the coils of said magnets, and means at the substation for controlling the circuit through said magnets for causing the operation of said switch.

36. In a telephone system, a central station, two substations, selecting switches in said central tation, a metallic talking circuit joining said substations through said central station, a source of current, magnets controlling said selecting switches and connected in bridge across said metallic circuit, means at one ofthe substations adapted to effect the energization of said magnets by said source of current, and two condensers in said central station, one serially connected in each of the conductors of said metallic circuit.

37. In a telephone system, a pair of metallic circuit subscribers lines leading to a central ofiice, selecting switches at said central office, trunk lines controlled by said selecting switches for connecting said pair of lines together, a pair of controlling magnets at each of said selecting switches bridged across the talking circuit between said two stations, a source of current adapted to supply current to the limbs of said line through said magnets, and means at one of the subscribers stations for closing the circuit through said magnets for the operation of said switches.

38. In a telephone system, two substations, a central station, selector switches, a connector switch, a metallic talkingcircuit connecting said substations through said central station, magnets for controlling said selector and connector switches bridged across said talking circuit, a source of current at said central station adapted to supply current through said magnets to the limbs of said metallic talking circuit, a return path for said source of current, and means at one of the substations for causing current to flow through all of said magnets simultaneously to cause the breaking up of said talking circuit and the returning of said selector switches to their normal position.

39. In an automatic telephone system, the combination with a telephone line, of a plurality of switches at the central oflice of the system having contacts for extending said line serially through said switches, a pair of relays at each switch having their coils normally bridged between the line strands and out of the path of voice currents when a talking circuit has been established, said relays for each switch serving to set the contacts of that switch into connection with the next succeeding switch, and a release circuit for each switch controlled by the simultaneous actuation ofsaid pair of relays of that switch.

' In an automatic telephone system, the combination with a telephone line, of a plurality of switches at the central otlicc of the system having contacts for extending succeeding switch, and means for interrupting the circuit by which one of said relays controls one of the setting up magnets after the relay has performed its setting up function. y

41. In a telephone system, a conductor, a plurality of automatic switches for serial connection in different combinations to extend said conductor in links from'one point to another through a plurality of said switches, a relay at each switch having a coil included in abranch from said conductor and actuated by current over said conductor to operate its associated switch to bring about the extension of said con- 15 ductor to the next link in the series, and means controlled bysaid relay at each switch for releasing the associated switch.

Signed by me at Chicago, county of Cook, State of Illinois, in the presence of 20 two witnesses.

BERT G. DUNHAM.

Witnesses:

SAMUEL G. MoMnEN, HAZAEL C. PRADo. 

